White, biaxially oriented, flame-retardant polyester film with cycloolefin copolymer, its use and process for its production

ABSTRACT

The present application relates to a white, biaxially oriented, flame-retardant polyester film with at least one base layer which comprises, based on the weight of the base layer, from 2 to 60% by weight of a cycloolefin copolymer (COC), where the glass transition temperature of the COC is within the range from 70 to 270° C. The film also comprises from 0.5 to 30% by weight of flame retardant, based on the weight of the layer comprising the flame retardant. The film of the invention is suitable for packing foods or other consumable items which are sensitive to light and/or to air, or for use in industry, e.g. in the production of hot-stamping foils or as a label film, or for image-recording papers, printed sheets or magnetic recording cards.

The present invention relates to a white, biaxially oriented,flame-retardant polyester film comprising at least one layer whichcomprises a polyester and a cycloolefin copolymer (COC). The inventionfurther relates to the use of the polyester film, and to a process forits production.

BACKGROUND OF THE INVENTION

White, biaxially oriented polyester films are known from the prior art.These known prior art films are either easy to produce, have goodoptical properties or have acceptable processing performance. DE-A 2 353347 describes a process for producing milky polyester film having one ormore layers, which comprises preparing a mixture from particles of alinear polyester with from 3 to 27% by weight of a homopolymer orcopolymer of ethylene or propylene, extruding the mixture as a film,quenching the film and biaxially orienting the film via orientation indirections running perpendicular to one another, and heat-setting thefilm. A disadvantage of this process is that regrind which arises duringproduction of the film (essentially a mixture of polyester and ethyleneor propylene copolymer) cannot be reused without yellowing the film.However, this makes the process uneconomic, but the film produced withregrind would not gain acceptance in the market. In addition, theroughness of the film is much too high, and this gives the film a verymatt appearance (very low gloss), undesirable for many applications.

EP-A 0 300 060 describes a single-layer polyester film which comprises,besides polyethylene terephthalate, from 3 to 40% by weight of acrystalline propylene polymer and from 0.001to 3% by weight of asurface-active substance. The effect of the surface-active substance isto increase the number of vacuoles in the film and at the same time toreduce their size to the desired extent. This gives the film greateropacity and lower density. A residual disadvantage of the film is thatregrind which arises during production of the film (essentially amixture of polyester and propylene homopolymer) cannot be reused withoutyellowing the film. However, this makes the film uneconomic, but thefilm produced with regrind would not gain acceptance in the market. Inaddition, the roughness of the film is much too high, giving it a verymatt appearance (very low gloss), undesirable for many applications.

EP-A 0 360 201 describes a polyester film having at least two layers andcomprising a base layer with fine vacuoles, with a density of from 0.4to 1.3 kg/dm3, and having at least one outer layer whose density isabove 1.3 kg/dm3. The vacuoles are achieved by adding from 4 to 30% byweight of a crystalline propylene polymer, followed by biaxialstretching of the film. The additional outer layer improves the ease ofproduction of the film (no streaking on the film surface), and thesurface tension is increased and the roughness of the laminated surfacecan be reduced. A residual disadvantage is that regrind arising duringproduction of the film (essentially a mixture of polyester and propylenehomopolymer) cannot be reused without yellowing the film. However, thismakes the process uneconomic, but the film produced with regrind wouldnot gain acceptance in the market. In addition, the roughnesses of thefilms listed in the examples are still too high, giving the films a mattappearance (low gloss), undesirable for many applications.

EP-A 0 795 399 describes a polyester film having at least two layers andcomprising a base layer with fine vacuoles, the density of which is from0.4 to 1.3 kg/dm3, and having at least one outer layer, the density ofwhich is greater than 1.3 kg/dm3. The vacuoles are achieved by addingfrom 5 to 45% by weight of a thermoplastic polymer to the polyester inthe base, followed by biaxial stretching of the film. The thermoplasticpolymers used are, inter alia, polypropylene, polyethylene,polymethylpentene, polystyrene or polycarbonate, and the preferredthermoplastic polymer is polypropylene. As a result of adding the outerlayer, ease of production of the film is improved (no streaking on thefilm surface), the surface tension is increased and the roughness of thelaminated surface can be matched to prevailing requirements. Furthermodification of the film in the base layer and/or in the outer layers,using white pigments (generally TiO2) and/or using optical brightenerspermits the properties of the film to be matched to the prevailingrequirements of the application. A residual disadvantage is that regrindWhich arises during production of the film (essentially a mixture ofpolyester and the added polymer) cannot be reused without undefined andhighly undesirable changes in the color of the film. This makes theprocess uneconomic, but the film produced with regrind would not gainacceptance in the market. In addition, the films listed in the examplescontinue to have excessive roughness values, giving them a mattappearance (low gloss), undesirable for many applications.

DE-A 195 40 277 describes a polyester film having one or more layers andcomprising a base layer with fine vacuoles, with a density of from 0.6to 1.3 kg/dm3, and having planar birefringence of from −0.02 to 0.04.The vacuoles are achieved by adding from 3 to 40% by weight of athermoplastic resin to the polyester in the base, followed by biaxialstretching of the film. The thermoplastic resins used are, inter alia,polypropylene, polyethylene, polymethylpentene, cyclic olefin polymers,polyacrylic resins, polystyrene or polycarbonate, preferred polymersbeing polypropylene and polystyrene. By maintaining the stated limitsfor the birefringence of the film, the film claimed has in particularsuperior tear strength and superior isotropy properties. However, aresidual disadvantage is that regrind arising during production of thefilm cannot be reused without undefined discoloration of the filmarising, and this in turn is highly undesirable. This makes the processuneconomic, but the film produced with regrind would not gain acceptancein the market. In addition, the roughnesses of the films listed in theexamples are still too high, giving them a matt appearance (low gloss),undesirable for many applications.

DE-A 23 46 787 describes a flame-retardant polymer. Besides the polymeritself, its use for producing films and fibers is also described.However, the following shortcomings were apparent during production offilms with this phospholane-modified polymer claimed in the DE-A:

The polymer is very sensitive to hydrolysis and has to be verythoroughly predried.

On drying with dryers of the prior art, the polymer coagulates, makingit extremely difficult, or even impossible, to produce a film.

The films produced, under conditions which are extreme and notcost-effective, embrittle when exposed to heat, i.e. their mechanicalproperties deteriorate sharply due to the rapid onset of embrittlement,making the film industrially unusable. This embrittlement arises afteras little as 48 hours of exposure to heat.

The object of the present invention was to provide a white, biaxiallyoriented polyester film which has high gloss and improved ease ofproduction, i.e. low production costs, and which moreover has good heatresistance and flame retardancy. In particular, it should be possiblefor cut material (regrind) directly associated with the film productionprocess to be reused in the production process at a concentration offrom 10 to 70% by weight, based on the total weight of the film, withoutany resultant adverse effect on the physical or optical properties ofthe film produced with regrind. In particular, addition of regrindshould not cause any significant yellowing of the film.

High flame retardancy means that in what is known as a fire protectiontest the white film meets the requirements of DIN 4102, Part 2 and inparticular the requirements of DIN 4102, Part 1 and can be classified inbuilding materials class B2, in particular B1, for low-flammabilitymaterials.

The film should moreover pass the UL 94 test known as the “Verticalburning test for flammability of plastic materials”, thereforequalifying for classification 94 VTM-0. This means that the film ceasesto burn within 10 seconds after removal of the bunsen burner, that nofurther smoldering is observed after 30 seconds, and that no flamingdrops are observed over the entire period.

Cost-effective production includes the capability of the polymers orpolymer components needed for producing the flame-retardant film to bedried using industrial dryers of the prior art. It is important that thepolymers do not cake and do not undergo thermal degradation. Theseindustrial dryers of the prior art include vacuum dryers, fluidized-beddryers, moving-bed dryers and fixed-bed dryers (power dryers). Thedryers mentioned operate at temperatures of from 100 to 170° C., atwhich flame-retardant polymers usually cake and have to be dug out,making film production impossible.

In vacuum dryers, which have the gentlest drying action, the polymerpasses through a range of temperature of from about 30 to 130° C. at apressure of 50 mbar. A process known as postdrying is then required, ina hopper at temperatures of from 100 to 130° C. and with a residencetime of from 3 to 6 hours. Even here, the known polymer cakes to anextreme extent.

Good heat resistance means that the film and its mechanical propertiesdo not deteriorate after 100 hours of annealing at 100° C. in acirculating-air heating cabinet.

DESCRIPTION OF THE INVENTION

According to the invention, the object is achieved by means of a white,biaxially oriented, flame-retardant polyester film with at least onebase layer made from polyester, the characterizing features of which arethat at least the base layer also comprises, based on the weight of thebase layer, from 2 to 60% by weight of a cycloolefin copolymer (COC),where the glass transition temperature of the cycloolefin copolymer(COC) is within the range from 70 to 270° C., and that the filmcomprises at least one flame retardant which is preferably fed directlyas a masterbatch to the polyester during film production.

The white, biaxially oriented polyester film as defined in the presentinvention is a film of this type whose whiteness is above 70%,preferably above 75% and particularly preferably above 80%. In addition,the opacity of the film of the invention is above 55%, preferably above60% and particularly preferably above 65%.

To achieve the desired whiteness of the film of the invention, theamount of COC in the base layer should be above 2% by weight, otherwisethe whiteness is below 70%. On the other hand, if the amount of COC isabove 60% by weight, the film is no longer cost-effective to produce,since the process of orienting the film becomes unreliable.

It is also necessary for the glass transition temperature of the COCused to be above 70° C. Otherwise, if the glass transition temperatureof the COC used is below 70° C., the polymer mixture is difficult toprocess, since it becomes difficult to extrude. The desired whiteness islost and use of regrind gives a film with a tendency toward increasedyellowness. On the other hand, if the glass transition temperature ofthe COC selected is above 270° C. the homogenization of the polymermixture in the extruder will no longer be sufficient. This then gives afilm with undesirably inhomogeneous properties.

In the preferred embodiment of the film of the invention, the glasstransition temperature of the COCs used is within the range from 90 to250° C., and in the particularly preferred embodiment it is within therange from 110 to 220 C.

Surprisingly, it has been found that a white, opaque, glossy film can beproduced by adding a COC in the manner described above.

The whiteness and the opacity of the film can be adjusted with precisionand adapted to particular requirements by varying the amount and natureof the COC added. This means that the use of other commonly usedwhitening or opacifying additives can substantially be dispensed with.It was also highly surprising that the surface roughness of the film issubstantially lower, and therefore the gloss of the film substantiallyhigher, than for comparable films of the prior art. A quite sensationaldiscovery was the additional effect that, despite the presence of flameretardant, regrind exhibits no tendency toward yellowing, as is observedwhen using polymeric additives and conventional flame retardants of theprior art.

None of the features described was foreseeable. This was particularlythe case since COC is evidently substantially incompatible withpolyethylene terephthalate and is known to require stretching ratios andstretching temperatures similar to those for polyethylene terephthalate.Under these circumstances the skilled worker would not have expectedthat a white, opaque film with high gloss could be produced under theseproduction conditions.

In the preferred and particularly preferred embodiments, the film of theinvention has high/particularly high whiteness and high/particularlyhigh opacity, while addition of regrind causes extremely little changein the color of the film.

The film of the invention comprises at least one flame retardant, whichis fed by way of what is known as masterbatch technology directly duringfilm production, the concentration of the flame retardant being withinthe range from 0.5 to 30.0% by weight, preferably from 1.0 to 20.0% byweight, based on the weight of the layer which comprises the flameretardant. During production of the masterbatch, the relationshipbetween flame retardant and thermoplastic is generally within the rangefrom 60% by weight:40% by weight to 10% by weight:90% by weight.

Typical flame retardants include bromine compounds, chloroparaffins andother chlorine compounds, antimony trioxide, and alumina trihydrates,the halogen compounds being disadvantageous since they producehalogen-containing byproducts. Other serious disadvantages are the lowlightfastness of films in which these compounds are present, and theevolution of hydrogen halides in the event of a fire.

Examples of suitable flame retardants used according to the inventionare organic phosphorus compounds, such as carboxyphosphinic acids,anhydrides thereof and dimethyl methylphosphonate.

Since the flame retardants generally have some degree of susceptibilityto hydrolysis, concomitant use of a hydrolysis stabilizer may beadvisable.

The hydrolysis stabilizers used are generally amounts of from 0.01 to1.0% by weight of phenolic stabilizers, of alkali metal/alkaline earthmetal stearates and/or of alkali metal/alkaline earth metal carbonates.The amounts of phenolic stabilizers used are preferably from 0.05 to0.6% by weight, in particular from 0.15 to 0.3% by weight, and theirmolar mass is preferably above 500 g/mol. Particularly advantageouscompounds are pentaerythrityltetrakis-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene.

It was therefore more than surprising that by using masterbatchtechnology and a suitable predrying and/or precrystallization procedureand, if desired, using small amounts of a hydrolysis stabilizer, it ispossible to produce a flame-retardant, thermoformable film with therequired property profile cost-effectively and especially without anycaking in the dryer, and that on exposure to high temperature the filmdoes not embrittle, and does not break when folded.

It was very surprising that, together with this excellent result andwith the flame retardancy required:

the Yellowness Index of the film undergoes no adverse change whencompared with that of an unstabilized film, within the bounds ofaccuracy of measurement;

there are no releases of gases, no die deposits and no framecondensation, and the film therefore has excellent optical propertiesand excellent profile and layflat;

the flame retardant, UV-resistant film has excellent stretchability, andtherefore can be produced in a reliable and stable manner on high-speedfilm lines at speeds of 420 m/min.

The film is therefore also cost-effective.

The film of the invention has one or more layers. Single-layerembodiments have a structure like that of the COC-containing layerdescribed below. Embodiments having more than one layer have at leasttwo layers and always comprise the COC-containing layer and at least oneother layer, where the COC-containing layer is the base layer but mayalso form the intermediate layer or the outer layer of the film havingtwo or more layers. In one preferred embodiment, the COC-containinglayer forms the base layer of the film with at least one outer layer andpreferably outer layers on both sides, and an intermediate layer orintermediate layers may be present, if desired, on one or both sides. Inanother preferred embodiment, the COC-containing layer also forms anintermediate layer of the multilayer film. Other embodiments withCOC-containing intermediate layers have a five-layer structure withCOC-containing intermediate layers on both sides of the COC-containingbase layer. In another embodiment, the COC-containing layer may form, aswell as the base layer, an outer layer or outer layers on the base layeror intermediate layer, on one or both sides. For the purposes of thepresent invention, the base layer is that layer which makes up more thanfrom 50 to 100%, preferably from 70 to 90%, of the total film thickness.The outer layer is always the layer which forms the outer layer of thefilm, and it is preferable for the invention if one or two outer layershave been arranged on the COC-containing base layer, and if the flameretardant is present in the outer layer(s).

Each embodiment of the invention is a non-transparent, white film. Forthe purposes of the present invention, non-transparent films are thosefilms whose light transmittance to ASTM D1003-77 is below 95%,preferably below 75%.

The COC-containing layer (the base layer) of the film of the inventioncomprises a polyester, preferably a polyester homopolymer, a COC, theflame retardant, and also, if desired, other additives, in each case ineffective amounts. This layer generally comprises at least 20% byweight, preferably from 40 to 98% by weight, in particular from 70 to96% by weight, of polyester, based on the weight of the layer.

The base layer of the film comprises, as main constituent, athermoplastic polyester. Polyesters suitable here are those made fromethylene glycol and terephthalic acid (=polyethylene terephthalate,PET), from ethylene glycol and naphthalene-2,6-dicarboxylic acid(=polyethylene 2,6-naphthalate, PEN), from1,4-bishydroxymethylcyclohexane and terephthalic acid(=poly-1,4-cyclohexanedimethylene terephthalate, PCDT) or else fromethylene glycol, naphthalene-2,6-dicarboxylic acid andbiphenyl4,4′-dicarboxylic acid (=polyethylene 2,6-naphthalatebibenzoate, PENBB). Particular preference is given to polyesters whichare composed of at least 90 mol %, preferably at least 95 mol %, ofethylene glycol units and terephthalic acid units or ethylene glycolunits and naphthalene-2,6-dicarboxylic acid units. The remaining monomerunits are derived from other aliphatic, cycloaliphatic or aromatic diolsand, respectively, dicarboxylic acids, as may also be present in layer A(A=outer layer 1) or in layer C (C=outer layer 2) of a multilayered ABC(B=base layer) film.

Examples of other suitable aliphatic diols are diethylene glycol,triethylene glycol, aliphatic glycols of the formula HO—(CH2)n—OH, wheren is an integer from 3 to 6 (in particular 1,3-propanediol,1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol) or branchedaliphatic glycols having up to 6 carbon atoms. Among the cycloaliphaticdiols, mention should be made of cyclohexanediols (in particular1,4-cyclohexanediol). Other suitable aromatic diols are those, forexample, of the formula HO—C6H4—X—C6H4—OH where X is —CH2—, —C(CH3)2—,—C(CF3)2—, —O—, —S— or —S02—. Bisphenols of the formula HO—C6H4—C6H4—OHare also highly suitable.

Other preferred aromatic dicarboxylic acids are benzenedicarboxylicacids, naphthalenedicarboxylic acids (such as naphthalene-1,4- or-1,6-dicarboxylic acid), biphenyl-x,x′-dicarboxylic acids (in particularbiphenyl-4,4′-dicarboxylic acid), diphenylacetylene-x,x′-dicarboxylicacids (in particular diphenylacetylene4,4′-dicarboxylic acid) andstilbene-x,x′-dicarboxylic acids. Among the cycloaliphatic dicarboxylicacids mention should be made of cyclohexanedicarboxylic acids (inparticular cyclohexane-1,4-dicarboxylic acid). Among the aliphaticdicarboxylic acids, the (C3-C19)-alkanedioic acids are particularlysuitable, where the alkane moiety may be straight-chain or branched.

The polyesters may, for example, be prepared by the transesterificationprocess. The starting materials here are dicarboxylic esters and diols,and these are reacted using the usual transesterification catalysts,such as salts of zinc, of calcium, of lithium, of magnesium or ofmanganese. The intermediates are then polycondensed in the presence oftypical polycondensation catalysts, such as antimony trioxide ortitanium salts. They may equally well be prepared by the directesterification process in the presence of polycondensation catalysts,starting directly from the dicarboxylic acids and the diols.

According to the invention, the COC-containing layer (base layer) or, inthe case of single-layer embodiments, the film, comprises an amount ofnot less than 4.0% by weight, preferably from 5 to 50% by weight andparticularly preferably from 6 to 40% by weight, of a cycloolefincopolymer (COC), based on the weight of the base layer or, in the caseof single-layer embodiments, based on the weight of the film. It issignificant for the present invention that the COC is not compatiblewith the polyethylene terephthalate and does not form a homogeneousmixture with the same.

Cycloolefin polymers are homopolymers or copolymers which containpolymerized cycloolefin units and, if desired, acyclic olefins ascomonomer. Cycloolefin polymers suitable for the present inventioncontain from 0.1 to 100% by weight, preferably from 10 to 99% by weight,particularly preferably from 50 to 95% by weight, of polymerizedcycloolefin units, in each case based on the total weight of thecycloolefin polymer. Particular preference is given to polymers whichhave been built up using the monomers comprising the cyclic olefins ofthe formulae I, II, III, IV, V or VI:

R1, R2, R3, R4, R5, R6, R7 and R8 in these formulae are identical ordifferent and are a hydrogen atom or a C1-C30-hydrocarbon radical, ortwo or more of the radicals R1 to R8 have been bonded cyclically, andthe same radicals in the different formulae may have the same or adifferent meaning. Examples of C1-C30-hydrocarbon radicals are linear orbranched C1-C8-alkyl radicals, C6-C18-aryl radicals, C7-C20-alkylenearylradicals and cyclic C3-C20-alkyl radicals and acyclic C2-C20-alkenylradicals.

If desired, the COCs may contain from 0 to 45% by weight, based on thetotal weight of the cycloolefin polymer, of polymerized units of atleast one monocyclic olefin of the formula VIl:

n here is a number from 2 to 10.

If desired, the COCs may contain from 0 to 99% by weight, based on thetotal weight of the COC, of polymerized units of an acyclic olefin ofthe formula VIII:

R9, R10, R11 and R12 here are identical or different and are a hydrogenatom or a C1-C10-hydrocarbon radical, e.g. a C1-C8-alkyl radical or aC6-C14-aryl radical.

Other polymers suitable in principle are cycloolefin polymers which areobtained by ring-opening polymerization of at least one of the monomersof the formulae I to VI, followed by hydrogenation.

Cycloolefin homopolymers have a structure composed of one monomer of theformulae I to VI. These cycloolefin polymers are less suitable for thepurposes of the present invention. Polymers suitable for the purposes ofthe present invention are cycloolefin copolymers (COC) which comprise atleast one cycloolefin of the formulae I to VI and acyclic olefins of theformula VIII as comonomer. Acyclic olefins preferred here are thosewhich have from 2 to 20 carbon atoms, in particular unbranched acyclicolefins having from 2 to 10 carbon atoms, for example ethylene,propylene and/or butylene. The proportion of polymerized units ofacyclic olefins of the formula VIII is up to 99% by weight, preferablyfrom 5 to 80% by weight, particularly preferably from 10 to 60% byweight, based on the total weight of the respective COC.

Among the COCs described above, those which are particularly preferredcontain polymerized units of polycyclic olefins having a fundamentalnor-bornene structure, particularly preferably norbornene ortetracyclododecene. Particular preference is also given to COCs whichcontain polymerized units of acyclic olefins, in particular ethylene.Particular preference is in turn given to norbornene-ethylene copolymersand tetracyclododecene-ethylene copolymers which in each case containfrom 5 to 80% by weight, preferably from 10 to 60% by weight, ofethylene (based on the weight of the copolymer).

The cycloolefin polymers generically described above generally haveglass transition temperatures Tg in the range from −20 to 400° C.However, COCs which can be used for the invention have a glasstransition temperature Tg above 70° C., preferably above 90° C. and inparticular above 110° C. The viscosity number (decalin, 135° C., DIN 53728) is advantageously from 0.1 to 200 ml/g, preferably from 50 to 150ml/g.

The COCs are prepared by heterogeneous or homogeneous catalysis withorganometallic compounds, as described in a wide variety of documents.Suitable catalyst systems based on mixed catalysts made from titaniumcompounds and, respectively, vanadium compounds in conjunction withaluminum organyl compounds are described in DD 109 224, DD 237 070 andEP-A-0 156 464. EP-A-0 283 164, EP-A-0 407 870, EP-A-0 485 893 andEP-A-0 503 422 describe the preparation of COCs with catalysts based onsoluble metallocene complexes. The preparation processes for COCsdescribed in the abovementioned specifications are expresslyincorporated herein by way of reference.

The COCs are incorporated into the film either in the form of puregranules or in the form of granulated concentrate (masterbatch), bypremixing the polyester granules or polyester powder with the COC or,respectively, with the COC masterbatch, followed by feeding to anextruder. In the extruder, the mixing of the components continues andthey are heated to the processing temperature. It is advantageous herefor the novel process if the extrusion temperature is above the glasstransition temperature Tg of the COC, generally above the glasstransition temperature of the COC by at least 5 K, preferably by from 10to 180 K, in particular by from 15 to 150 K.

For the intermediate layers and for the outer layers, it is possible inprinciple to use the polymers used for the base layer. Besides these,other materials may also be present in the outer layers, and the outerlayers are then preferably composed of a mixture of polymers or of acopolymer or of a homopolymer which comprise ethylene 2,6-naphthalateunits and ethylene terephthalate units. Up to 30 mol % of the polymersmay be composed of other comonomers (e.g. ethylene isophthalate units).

The base layer and the other layers may additionally compriseconventional additives, such as stabilizers, antiblocking agents andother fillers. They are advantageously added to the polymer or,respectively, to the polymer mixture prior to melting. Examples ofstabilizers used are phosphorus compounds, such as phosphoric acid orphosphoric esters.

Typical antiblocking agents (in this context also termed pigments) areinorganic and/or organic particles, such as calcium carbonate, amorphoussilica, talc, magnesium carbonate, barium carbonate, calcium sulfate,barium sulfate, lithium phosphate, calcium phosphate, magnesiumphosphate, aluminum oxide, lithium fluoride, the calcium, barium, zincor manganese salts of the dicarboxylic acids used, carbon black,titanium dioxide, kaolin or crosslinked polymer particles, e.g.polystyrene particles or acrylate particles.

The additives selected may also comprise mixtures of two or moredifferent antiblocking agents or mixtures of antiblocking agents of thesame composition but different particle sizes. The particles may beadded to the polymers of the individual layers of the film in therespective advantageous amounts, e.g. as a glycolic dispersion duringthe polycondensation or via masterbatches during extrusion. Pigmentconcentrations which have proven particularly suitable are from 0 to 25%by weight (based on the weight of the respective layer). EP-A-0 602 964,for example, describes the antiblocking agents in detail.

To improve the whiteness of the film, the base layer or the otheradditional layers may comprise further pigmentation. It has provenparticularly advantageous here for the additional materials added to bebarium sulfate with a particle size of from 0.3 to 0.8 μm, preferablyfrom 0.4 to 0.7 μm, or titanium dioxide with a particle size of from0.05 to 0.3 μm. This gives the film a brilliant white appearance. Theconcentration of barium sulfate or titanium dioxide is within the rangefrom 1 to 25% by weight, preferably from 1 to 20% by weight, and verypreferably from 1 to 15% by weight.

The total thickness of the film may vary within wide limits and dependson the application envisaged. The preferred embodiments of the novelfilm have total thicknesses of from 4 to 400 μm, preferably from 8 to300 μm, particularly preferably from 10 to 300 μm. The thickness of anyintermediate layer(s) present is/are, in each case independently of oneanother, from 0.5 to 15 μm, preferably from 1 to 10 μm, in particularfrom 1 to 8 μm. All the values given are based on one intermediatelayer. The thickness of the outer layer(s) is selected independently ofthe other layers and is preferably within the range from 0.1 to 10 μm,in particular from 0.2 to 5 μm, preferably from 0.3 to 2 μm, and outerlayers applied on both sides may be identical or different in terms oftheir thickness and composition. The thickness of the base layer istherefore given by the difference between the total thickness of thefilm and the thickness of the outer and intermediate layer(s) applied,and, similarly to the total thickness, may therefore vary within widelimits.

In one particular embodiment, the outer layers may also be composed of apolyethylene naphthalate homopolymer, or of an ethyleneterephthalate-ethylene naphthalate copolymer, or of a compound.

In this embodiment, the standard viscosity of the thermoplastics of theouter layers is similar to that of the polyethylene terephthalate of thebase layer.

In the embodiments having two or more layers, the flame retardant ispreferably present in the base layer. However, the outer layers may, ifrequired, also have flame retardant.

In another embodiment, flame retardant may be present in the outerlayers. If required, or if fire-protection requirements are stringent,the base layer may additionally comprise what is known as a base levelof flame retardant.

Unlike in the single-layer embodiment, the amount of flame retardanthere in percent by weight is based on the weight of the respective layerhaving the agents.

It is also surprising that fire tests to DIN 4102 Part 1 and Part 2, andalso the UL 94 test, have shown that films of the invention comply withthe requirements.

The flame-retardant films having two or more layers and produced byknown coextrusion technology are therefore of great interest in economicterms when compared with monofilms provided with full flame retardancy,since markedly less additives are needed to achieve comparable flameretardancy.

During production of the film it was found that the flame-retardant filmgives excellent longitudinal and transverse orientation withoutbreak-offs. In addition, no gas releases of any type attributable to thepresence of flame retardant were found, and this is important for theinvention, since most conventional flame retardants evolve veryundesirable and unpleasant gases, attributable to the decomposition ofthese compounds under the conditions of processing, at extrusiontemperatures above 260° C., and are therefore of no use.

Surprisingly, even films of the invention in the range of thickness from5 to 300 μm comply with requirements for the construction materialsclass B1 to DIN 4102 Part 1 and with those for the UL 94 test.

During production of the white, flame-retardant film it was also foundthat the flame retardant can be incorporated using masterbatchtechnology and suitable predrying and/or precrystallization of the flameretardant masterbatch without the occurrence of caking in the dryer, andtherefore the film can be produced cost-effectively.

It was more than surprising that incorporation is made even easier bysmall additions of a hydrolysis stabilizer within the flame retardantmasterbatch. Throughputs, and therefore production rates, could readilybe increased in this way. In one very specific embodiment, the film alsocomprises small amounts of a hydrolysis stabilizer in the layers havingflame retardant.

Measurements showed that the film of the invention does not embrittleover long periods at high temperatures of 100° C., a fact which is morethan surprising. This result is attributable to the synergistic actionof suitable precrystallization, predrying, masterbatch technology andprovision of flame retardant.

The film of the invention can moreover readily be recycled withoutpollution of the environment and without loss of mechanical properties,and examples of uses for which it is suitable are therefore short-livedpromotional placards for constructing exhibition stands and otherpromotional requisites where fire protection is desirable.

The invention further provides a process for producing the polyesterfilm of the invention by the extrusion or coextrusion process known perse.

According to the invention, the flame retardant, with or without thehydrolysis stabilizer, is fed by way of masterbatch technology. Theflame retardant is fully dispersed in a carrier material. Carriermaterials which may be used are the polyester itself, e.g. thepolyethylene terephthalate, or else other polymers compatible with thepolyester.

It is important in masterbatch technology that the particle size and thebulk density of the masterbatch are similar to the particle size and thebulk density of the polyester, so that homogeneous distribution isachieved, giving uniform stabilization.

The polyester films may be produced by known processes from polyesterwith, if desired, other polymers, with the flame retardant, with orwithout the hydrolysis stabilizer and/or with other customary additivesin customary amounts of from 1.0 to a maximum of 30% by weight, eitherin the form of a monofilm or else in the form of, if desired coextruded,films having two or more layers and with identically or differentlyconstructed surfaces, where one surface may have been pigmented, forexample, but no pigment is present at the other surface. Known processesmay also have been used to provide one or both surfaces of the film witha conventional functional coating.

It is important for the invention that the masterbatch which comprisesthe flame retardant and, if used, the hydrolysis stabilizer, isprecrystallized or predried. This predrying includes gradual heating ofthe masterbatch at reduced pressure (from 20 to 80 mbar, preferably from30 to 60 mbar, in particular from 40 to 50 mbar) with agitation, and, ifdesired, post-drying at a constant, elevated temperature, again atreduced pressure. It is preferable for the masterbatch to be charged atroom temperature from a metering vessel in the desired blend togetherwith the polymer of the base and/or outer layers and, if desired, withother raw material components batchwise into a vacuum dryer in which thetemperature profile moves from 10 to 160° C., preferably from 20 to 150°C., in particular from 30 to 130° C., during the course of the dryingtime or residence time. During the residence time of about 6 hours,preferably 5 hours, in particular 4 hours, the raw material mixture isstirred at from 10 to 70 rpm, preferably from 15 to 65 rpm, inparticular from 20 to 60 rpm. The resultant precrystallized or predriedraw material mixture is post-dried in a downstream vessel, likewiseevacuated, at temperatures of from 90 to 180° C., preferably from 100 to170° C., in particular from 110 to 160° C., for from 2 to 8 hours,preferably from 3 to 7 hours, in particular from 4 to 6 hours.

For the coextrusion process, the procedure is that the melt(s)corresponding to the single-layer film or to the individual layers ofthe film is/are extruded/coextruded through a flat-film die, theresultant film is drawn off for solidification on one or more rolls, thefilm is then biaxially stretched (oriented), and the biaxially stretchedfilm is then heat-set and, if desired, corona- or flame-treated on thesurface layer intended for further treatment.

The biaxial orientation is generally carried out in succession. Forthis, it is preferable to orient first longitudinally (i.e. in MD, themachine direction) and then transversely (i.e. in TD, perpendicularly tothe machine direction). This orientates the molecular chains. Thelongitudinal orientation preferably takes place with the aid of tworolls rotating at different rates corresponding to the desiredstretching ratio. For the transverse stretching, an appropriate suitabletenter frame is generally used.

Simultaneous orientation of the film of the invention in the twodirections (MD and TD) with the aid of a tenter frame suitable for thispurpose has proven not to be appropriate, since this stretching methodgives a film which has insufficient whiteness and insufficient opacity.

The temperature at which the orientation is carried out may be variedover a relatively wide range and depends on the properties desired inthe film. In general, the longitudinal stretching is carried out at from80 to 130° C. and the transverse stretching at from 90 to 150° C. Thelongitudinal stretching ratio is generally within the range from 2.5:1to 6:1, preferably from 3:1 to 5.5:1. The transverse stretching ratio isgenerally within the range from 3.0:1 to 5.0:1, preferably from 3.5:1 to4.5:1.

In the heat-setting which follows, the film is held at a temperature offrom 150 to 250° C. for from about 0.1 to 10 s. The film is then cooledand then wound up in the usual manner.

To establish other desired properties, the film may be chemicallytreated or else corona- or, respectively, flame-treated. The intensityof treatment is selected such that the surface tension of the film isgenerally above 45 mN/m.

To establish other properties, the film may also be coated. Typicalcoatings have adhesion-promoting, antistatic, slip-improving or releaseaction. It is clear that these additional coatings may be applied to thefilm by in-line coating using aqueous dispersions, prior to thetransverse stretching procedure.

The particular advantage of the novel film is its high whiteness andhigh opacity, together with good flame retardancy. Surprisingly, thegloss of the film was also very high. The whiteness of the film is above70%, preferably above 75% and particularly preferably above 80%. Theopacity of the novel film is above 55%, preferably above 60% andparticularly preferably above 65%. The gloss of the novel film is above80, preferably above 90 and particularly preferably above 100.

Another particular advantage of the invention is that regrind materialproduced directly during the production process can be reused at aconcentration of from 10 to 70% by weight, based on the total weight ofthe film, without any significant negative effect on the physicalproperties of the film. In particular, the regrinded material (composedessentially of polyester and COC) does not give undefined changes in thecolor of the film, as is the case in the films of the prior art.

A further advantage of the invention is that the production costs of thenovel film are comparable with those of conventional opaque films of theprior art. The other properties of the novel film relevant to itsprocessing and use remain essentially unchanged or are even improved.

The film has excellent suitability for packing foods or other consumableitems which are sensitive to light and/or to air. It is also highlysuitable for use in the industrial sector, e.g. for producinghot-stamping foils or as a label film. Besides this, the film is, ofcourse, particularly suitable for image-recording papers, printedsheets, magnetic recording cards, to name just a few possibleapplications.

The processing performance and winding performance of the film, inparticular on high-speed machines (winders, metallizers, printingmachines and laminating machines) is exceptionally good. A measure ofprocessing performance is the coefficient of friction of the film, whichis below 0.6. A decisive factor affecting winding performance, besides agood thickness profile, excellent layflat and a low coefficient offriction, is the roughness of the film. It has become apparent that thewinding of the novel film is particularly good if the average roughnessis within the range from 50 to 250 nm while the other properties arecomplied with. The roughness may be varied within the stated range by,inter alia, varying the COC concentration and the process parameters inthe production process.

The most important film properties according to the invention are againsummarized at a glance in the table below (Table 1), thus providing aparticularly clear picture.

TABLE 1 Range according Particularly to the invention Preferredpreferred Unit Test method Composition Concentration of cycloolefin 2-604-50 6-40 % copolymer (COC) in base layer Glass transition temperature70-270 90-250 110-220  ° C. DIN 73 765 of cycloolefin copolymer (COC)Flame retardant 0.5-30   1.0-20   % DIN 4102 Film propertiesWhiteness >70 >75 >80 % Berger Opacity >55 >60 >65 % DIN 53 146 COF <0.6<0.55 <0.5 DIN 53 375 Gloss >80 >90 >100 DIN 67 530 Average roughness Ra50-250 60-230 70-200 nm DIN 4768, cut-off of 0.25 mm

The following values were measured to characterize the polymers and thefilms:

SV (DCA), IV (DCA)

The standard viscosity SV (DCA) is measured in dichloroacetic acid byanalogy with DIN 53726.

The intrinsic viscosity (IV) is calculated as follows from the standardviscosity (SV)

IV(DCA)=6.67·10-4 SV(DCA)+0.118

Yellowness Index

The Yellowness Index YID is the deviation from the colorless state inthe “yellow” direction and is measured to DIN 6167.

Fire Performance

Fire performance is determined to DIN 4102, Part 2, constructionmaterials class B2, and to DIN 4102, Part 1, construction materialsclass B1, and also by the UL 94 test.

Coefficient of Friction

Coefficient of friction is determined to DIN 53 375. The coefficient ofsliding friction was determined 14 days after production.

Surface Tension

Surface tension was determined by what is known as the ink method (DIN53 364).

Roughness

Roughness Ra of the film was determined to DIN 4768 with a cut-off of0.25 mm.

Whiteness and Opacity

Whiteness and opacity were determined with the aid of a Zeiss,Oberkochem (DE) “ELREPHO” electric reflectance photometer, standardilluminant C, 2° normal observer. Opacity is determined to DIN 53 146.Whiteness is defined as W=RY+3RZ−3RX. W=whiteness, RY, RZ andRX=relevant reflection factors when the Y, Z and X color-measurementfilter is used. The white standard used was a barium sulfate pressing(DIN 5033, Part 9). A detailed description is given, for example, inHansl Loos “Farbmessung” [Color measurement], Verlag Beruf und Schule,Itzehoe (1989).

Light Transmittance

Light transmittance is measured using a method based on ASTM D1033-77.

Gloss

Gloss was determined to DIN 67 530. The reflectance was measured as anoptical value characteristic of a film surface. Based on the standardsASTM-D 523-78 and ISO 2813, the angle of incidence was set at 60°. Abeam of light hits the flat test surface at the set angle of incidenceand is reflected and/or scattered by this surface. A proportionalelectrical variable is displayed representing light beams hitting thephoto-electronic detector. The value measured is dimensionless and mustbe stated together with the angle of incidence.

Glass Transition Temperature

The glass transition temperature Tg was determined using film specimenswith the aid of DSC (differential scanning calorimetry) (DIN 73 765). ADuPont DSC 1090 was used. The heating rate was 20 K/min and the specimenweight was about 12 mg. The glass transition Tg was determined in thefirst heating procedure. Many of the specimens showed an enthalpyrelaxation (a peak) at the beginning of the step-like glass transition.The temperature taken as Tg was that at which the step-like change inheat capacity—without reference to the peak-shaped enthalpyrelaxation—achieved half of its height in the first heating procedure.In all cases, there was only a single glass transition observed in thethermogram in the first heating procedure.

EXAMPLE 1 (INVENTIVE)

Chips of polyethylene terephthalate (prepared by the transesterificationprocess using Mn as transesterification catalyst, Mn concentration: 100ppm) were dried at 150° C. to a residual moisture below 100 ppm and fedto the extruder for the base layer B Alongside this, chips of ®Topas6015 cycloolefin copolymer (COC) from Ticona (COC composed of2-norbornene and ethylene, see also W. Hatke: Folien aus COC [COCFilms], Kunststoffe 87 (1997) 1, pp. 58-62) with a glass transitiontemperature Tg of about 160° C. were also fed to the extruder for thebase layer B. The proportional amount of the cycloolefin copolymer (COC)in the entire film was 10% by weight. 4% by weight ofphosphorus-containing flame retardant were also added.

The flame retardant is the organic phosphorus compound dimethylmethylphosphonate, ®Amgard P 1045 from Albright & Wilson, which issoluble in PET.

According to the invention, the flame retardant is fed in the form of amasterbatch. The masterbatch is composed of 20% by weight of flameretardant and 80% by weight of PET with a standard viscosity SV (DCA) of810.

The masterbatch had a bulk density of 750 kg/m3. Extrusion followed bystepwise longitudinal and transverse orientation was used to produce awhite, opaque, single-layer film with an overall thickness of 23 μm.

Base layer B was a mixture of:

86.0% by weight of polyethylene terephthalate homopolymer with an SV of800 10.0% by weight of cycloolefin copolymer (COC) from Ticona, Topas6015 4.0% by weight of Amgard P 1045 The production conditions in theindividual steps of the process were: Extrusion: Temperatures Baselayer: 280° C. Take-off roll temperature: 30° C. LongitudinalTemperature: 80-125° C. stretching: Longitudinal stretching ratio: 4.2Transverse Temperature: 80-135° C. stretching: Transverse stretchingratio: 4 Setting: Temperature: 230° C. Duration: 3 s

The film had the required good properties and the desired handlingproperties, and the desired processing performance. The propertiesachieved in films produced in this way are shown in Table 2.

EXAMPLE 2 (INVENTIVE)

A change was made from Example 1 by adding 50% by weight of regrind tothe base layer. The amount of COC in the film thus produced was again10% by weight, and the amount of flame retardant was 4% by weight. Theprocess parameters were unchanged from Example 1. A visual observationwas made of any yellow coloration of the film. It can be seen from Table2 that hardly any yellow coloration of the film could be observed.

Base layer B was a mixture of:

43.0% by weight of polyethylene terephthalate homopolymer with an SV of800 50.0% by weight of regrind (86% by weight of polyester + 10% byweight of Topas 6015 + 4% by weight of Amgard P 1045) 5.0% by weight ofcycloolefin copolymer (COC) from Ticona, Topas 6015 2.0% by weight ofAmgard P 1045

EXAMPLE 3 (INVENTIVE)

Example 1 was now modified by producing a film of thickness 96 μm. Theamount of COC in the film was 8% by weight, and the amount of flameretardant was 4% by weight. The process parameters were unchanged fromExample 1. Avisual observation was made of any yellow coloration of thefilm. It can be seen from Table 2 that no yellow coloration of the filmwas observed.

Base layer B was a mixture of:

88.0% by weight of polyethylene terephthalate homopolymer with an SV of800 8.0% by weight of cycloolefin copolymer (COC) from Ticona, Topas6015 4.0% by weight of Amgard P 1045

EXAMPLE 4 (INVENTIVE)

A change was made from Example 3 by adding 50% by weight of regrind tothe base.

The amount of COC in the film was again 8% by weight, and the amount offlame retardant was 4% by weight. The process parameters were unchangedfrom Example 1. A visual observation was made of any yellow colorationof the film. It can be seen from Table 2 that hardly any yellowcoloration of the film could be observed.

Base layer B was a mixture of:

44.0% by weight of polyethylene terephthalate homopolymer with an SV of800 50.0% by weight of self-generated regrind (86% by weight ofpolyester + 10% by weight of Topas 6015 + 4% by weight of Amgard P 1045)4.0% by weight of cycloolefin copolymer (COC) from Ticona, Topas 60152.0% by weight of Amgard P 1045

COMPARATIVE EXAMPLE 1

Example 1 from DE-A 2 353 347 was repeated. The example was modifiedwith concomitant use of 50% by weight of regrind. It can be seen fromTable 2 that marked yellow coloration of the film was observed. Inaddition, the roughness of the film is much too high for manyapplications, and the gloss is too low for many applications. It ishighly probable that this is attributable to the use of other polymericadditives.

Base layer B was a mixture of:

47.5% by weight of polyethylene terephthalate homopolymer with an SV of800 50.0% by weight of self-generated regrind (95% by weight ofpolyester + 5% by weight of polypropylene) 2.5% by weight ofpolypropylene

COMPARATIVE EXAMPLE 2

Example 1 from EP-A 0 300 060 was repeated. The example was modifiedwith concomitant use of 50% by weight of regrind. It can be seen fromTable 2 that marked yellow coloration of the film was observed. Inaddition, the roughness of the film is much too high for manyapplications, and the gloss is too low for many applications. It ishighly probable that this is attributable to the use of other polymericadditives.

Base layer B was a mixture of:

45.0% by weight of polyethylene terephthalate homopolymer with an SV of800 50.0% by weight of self-generated regrind (95% by weight ofpolyester + 5% by weight of polypropylene) 5.0% by weight ofpolypropylene

COMPARATIVE EXAMPLE 3

Example 1 from EP-A 0 360 201 was repeated. The example was modifiedwith concomitant use of 50% by weight of regrind. It can be seen fromTable 2 that marked yellow coloration of the film was observed. Inaddition, the roughness of the film is much too high for manyapplications, and the gloss is too low for many applications. It ishighly probable that this is attributable to the use of other polymericadditives.

Base layer B was a mixture of:

40.0% by weight of polyethylene terephthalate homopolymer with an SV of800 50.0% by weight of self-generated regrind (95% by weight ofpolyester + 5% by weight of polypropylene) 10.0% by weight ofpolypropylene

COMPARATIVE EXAMPLE 4

Example 1 from DE-A 195 40 277 was repeated. The example was modifiedwith concomitant use of 50% by weight of regrind. It can be seen fromTable 2 that marked yellow coloration of the film was observed. Inaddition, the roughness of the film is much too high for manyapplications, and the gloss is too low for many applications. It ishighly probable that this is attributable to the use of other polymericadditives.

Base layer B was a mixture of:

43.5% by weight of polyethylene terephthalate homopolymer with an SV of800 50.0% by weight of self-generated regrind (95% by weight ofpolyester + 5% by weight of polystyrene) 6.5% by weight of polystyrene

TABLE 2 Coeffi- cient of Average Additive Glass Evalu- frict-ionroughness Film concen- transition ation of COF Ra thick- Layer trationin temperature of White- film Side A nm Ex- ness struc- Added to baselayer additive ness Opacity yellow- against Side Side ample μm turepolyester % ° C. % % ness Gloss Side C A C E1 23 B COC 10 170 75 75 ++115 0.52 120 120 E2 23 B COC 10 170 76 80 + 120 0.50 110 110 E3 96 B COC8 170 85 85 ++ 125 0.42 100 100 E4 96 B COC 8 170 86 90 + 130 0.35 98 98CE 1 155 B Polypropylene 5 −10 80 70 − 46 0.45 410 410 CE 2 100 BPolypropylene 10 −10 88 80 − 57 0.45 180 180 CE 3 100 ABA Polypropylene20 −10 92 89 − 54 0.25 370 370 CE 4 125 B Polystyrene 13 100 82 82 − 510.35 480 480 Key to yellowness in films produced: ++ : no yellowingdetectable + : slight yellow coloration detectable − : marked yellowcoloration detectable

Each of the films produced in Examples 1 to 4 and Comparative Examples 1to 4 was treated at a temperature of 100° C. for 200 hours in acirculating-air drying cabinet. The mechanical properties of the filmsof Examples 1 to 4 are unchanged. The films show not even the slightestsign of embrittlement phenomena, whereas the films of the comparativeexamples have cracks visible to the naked eye and attempts to fold themlead to fracture.

The films of Examples 1 to 4 comply with the requirements forconstruction material classes B 2 and B 1 to DIN 4102 Part 2/Part 1, andthey pass the UL 94 test, but this is not true for the films ofComparative Examples 1 to 4.

What is claimed is:
 1. A white, biaxially oriented, flame-retardantpolyester film comprising at least one polyester layer, wherein at leastthis layer comprises, based on the weight of this layer, from 4 to 60%by weight of a cycloolefin copolymer (COC), selected from the groupconsisting of norbornene/ethylene copolymers andtetracyclododecene/ethylene copolymers with an ethylene content of 5 to80% by weight where the glass transition temperature of the COC iswithin the range from 110 to 270° C., and wherein the layer comprises atleast one organic phosphorus compound as a flame retardant; saidpolyester film containing from about 10-70% by weight regrind.
 2. Thepolyester film as claimed in claim 1, wherein the COC has a glasstransition temperature within the range from 110 to 250° C., and whereinthe amount of flame retardant is within the range from 0.5 to 30% byweight, based on the weight of the layer comprising the flame retardant.3. The polyester film as claimed in claim 1, wherein the cycloolefincopolymer (COC) has a glass transition temperature within the range from110 to 220° C.
 4. The polyester film as claimed in claim 3, wherein theorganic phosphorus compounds are soluble in polyethylene terephthalate.5. The polyester film as claimed in claim 1, wherein the whiteness ofthe film is above 70%.
 6. The polyester film as claimed in claim 1,wherein the opacity of the film is above 55%.
 7. The polyester film asclaimed in claim 1, wherein the gloss of the film is above
 80. 8. Thepolyester film as claimed in claim 1, wherein the layer comprises from0.5 to 25 percent by weight of vocuole-inducing filler or white fillersor pigment or vacuole-inducing filler and white filler orvacuole-inducing filler and white pigment, in each case based on theweight of layer.
 9. The polyester film as claimed in claim 1, wherein atleast one outer layer has been arranged on the COC-containing layer, andwherein the flame retardant is present in the outer layer(s).
 10. Thepolyester film as claimed in claim 9, wherein an intermediate layer hasbeen arranged between the COC-containing layer and the outer layer. 11.The polyester film as claimed in claim 1, wherein the film has one layerand is composed of the COC-containing layer.
 12. A white, biaxiallyoriented, flame-retardant polyester film comprising at least onepolyester layer, which comprises, based on the weight of this layer,from 2 to 60% by weight of COC, selected from the group consisting ofnorbornene/ethylene copolymers and tetracyclododecene/ethylenecopolymers with an ethylene content of 5 to 80% by weight where theopacity of the film is above 60%, wherein the film also comprises anamount within the range from 1 to 20% by weight of a an organicphosphorus flame retardant, based on the weight of the layer comprisingthe flame retardant, and wherein the glass transition temperature of theCOC is within the range from 110 to 270° C.; said polyester filmcontaining from about 10-70% by weight regrind.
 13. A white, biaxiallyoriented, flame-retardant polyester film comprising at least onepolyester layer, which comprises, based on the weight of this layer,from 2 to 60% by weight of COC, selected from the group consisting ofnorbornene/ethylene copolymers and tetracyclododecene/ethylenecopolymers with an ethylene content of 5 to 80% by weight and thewhiteness of which is above 70%, wherein the film also comprises anamount within the range from 1 to 20% by weight of a an organicPhosphorus flame retardant, based on the weight of the layer comprisingthe flame retardant and wherein the glass transition temperature of theCOC is within the range from 110 to 270° C.; said polyester filmcontaining from about 10-70% by weight regrind.
 14. A white, biaxiallyoriented, flame-retardant polyester film comprising at least onepolyester layer, which comprises, based on the weight of this layer,from 2 to 60% by weight of COC, selected from the group consisting ofnorbornene/ethylene copolymers and tetracyclododecene/ethylenecopolymers with an ethylene content of 5 to 80% by weight, and the glossof which is above 80, wherein the film also comprises an amount withinthe range from 1 to 20% by weight of a an organic phosphorus flameretardant, based on the weight of the layer comprising the flameretardant and wherein the glass transition temperature of the COC iswithin the range from 110 to 270° C.; said polyester film containingfrom about 10-70% by weight regrind.
 15. The polyester film as claimedin claim 1, wherein the flame retardant is dimethyl methylphosphonate.